1. Field of the Invention
This invention relates to trimethyl(ethylcyclopentadienyl)platinum (C.sub.2 H.sub.5 C.sub.5 H.sub.4)Pt(CH.sub.3).sub.3, a process for producing the same and a process for producing platinum-containing films by the chemical vapor deposition method (hereinafter referred to simply as "the CVD method") by using the same.
2. Description of the Prior Art
With the recent tendency toward ultra-large-scale integrated circuits (ULSI), studies are under way to develop (Ba, Sr)TiO.sub.3 films having high dielectric constants, ferroelectric Pb(Zr,Ti)O.sub.3 films, SrBi.sub.2 Ta.sub.2 O.sub.9 films, etc. as capacitors. Also, investigations are in progress on Pt films to be used as electrodes therefor.
Although it has been a practice to produce these Pt films by the Pt metal sputtering method, it is expected that the desired step coverage or mass-productivity in further microscaled cases can be achieved by the CVD method. As the volatile Pt compounds to be used in the CVD method, investigations are in progress on trimethyl(cyclopentadienyl)platinum (C.sub.5 H.sub.5)Pt(CH.sub.3).sub.3, trimethyl(methylcyclopentadienyl)platinum (CH.sub.3 C.sub.5 H.sub.4)Pt(CH.sub.3).sub.3, cyclopentadienyl(allyl)platinum (C.sub.5 H.sub.5)Pt(C.sub.3 H.sub.5), dimethyl(cyclooctadiene)platinum (C.sub.8 H.sub.12)Pt(CH.sub.3).sub.2, methyl(carbonyl)cyclopentadienylplatinum (C.sub.5 H.sub.5)Pt(CH.sub.3)(CO), trimethyl(acetylacetonato)platinum (C.sub.5 H.sub.7 O.sub.2)Pt(CH.sub.3).sub.3, bis(acetylacetonato)platinum Pt(C.sub.5 H.sub.7 O.sub.2).sub.2, etc. In addition, there are platinum compounds containing phosphorus P, fluorine F or chlorine Cl. However, these compounds are omitted herein, since they are unfavorable in producing silicone semiconductors.
Y. J. Chen and H. D. Kaesz Appl. Phys. Lett., Vol. 53, 1591 (1988)! disclosed that starting with trimethyl (cyclopentadienyl)platinum (C.sub.5 H.sub.5)Pt(CH.sub.3).sub.3, a Pt film was formed on an Si substrate at 180.degree. C. in a hydrogen atmosphere at 1 atm by the CVD method by sublimating the feedstock from a source at 25.degree. C. together with an Ar gas. The obtained film was a bright one showing a high reflectance and being contaminated with not more than 1 atomic % of carbon, when examined by the XPS analysis.
However, (C.sub.5 H.sub.5)Pt(CH.sub.3).sub.3 has a melting point of 108.degree. C. and, therefore, is in the form of solid crystals at room temperature. It shows a vapor pressure of 0.1 Torr and 1 Torr respectively at around 31.degree. C. and 58.degree. C. Thus, it is to be supplied by sublimation.
Z. Xue, M. J. Strouse, D. K. Shuh, C. B. Knobler, H. D. Kaesz, R. F. Hicks and R. S. Williams J. Am. Chem. Soc., Vol. 111, 8779 (1989)! disclosed that starting with trimethyl(methylcyclopentadienyl)platinum (CH.sub.3 C.sub.5 H.sub.4)Pt(CH.sub.3).sub.3, a Pt film was formed on an Si substrate at 120.degree. C. by the CVD method by sublimating the feedstock from a source at 23.degree. C. together with an Ar gas and simultaneously feeding a hydrogen gas into a thermal decomposition chamber to give an atmosphere containing about 20% of hydrogen (1 atm). The obtained film was a bright one showing a high reflectance and being contaminated with not more than 1 atomic % of carbon, when examined by the XPS analysis.
However, (CH.sub.3 C.sub.5 H.sub.4)Pt(CH.sub.3).sub.3 has a melting point of 30.degree. C. and, therefore, is in the form of solid crystals at room temperature. It shows a vapor pressure of 0.1 Torr and 1 Torr respectively at around 30.degree. C. and 56.degree. C. Thus, it is to be supplied by evaporation or sublimation. Although trimethyl(methylcyclopentadienyl)platinum liquefies upon heating, it turns into the solid again when cooled to room temperature, which makes it necessary to provide countermeasure with respect to apparatus.
U.S. Pat. No. 5,130,172 has disclosed a process for coating a substrate with a metal comprising: maintaining the substrate at a temperature up to 190.degree. C.; exposing this substrate to a vaporized organometallic compound represented by the formula L.sub.n MR.sub.m obtained by heating to a temperature up to 100.degree. C.; then exposing the substrate to hydrogen gas at a temperature up to 100.degree. C.; and reacting the organometallic compound with hydrogen to thereby form a metal film. In the above formula L.sub.n MR.sub.m, L is hydrogen, ethylene, allyl, methylallyl, butadienyl, pentadienyl, cyclopentadienyl, methylcyclopentadienyl, cyclohexadienyl, hexadienyl, cycloheptatrienyl or derivatives of these compounds each having at least one alkyl side chain having less than five carbon atoms; M is a metal that can readily cycle between two oxidation states and can catalyze hydrogenation of hydrocarbon ligands; R is methyl, ethyl, propyl or butyl; n is an integer from 0 to the valence of the metal; m is an integer from 0 to the valence of the metal; and m plus n must equal the valence of the metal.
The Pt compounds given in the claims specifying the same are trimethyl(cyclopentadienyl)platinum (C.sub.5 H.sub.5)Pt(CH.sub.3).sub.3, trimethyl(methylcyclopentadienyl)platinum (CH.sub.3 C.sub.5 H.sub.4)Pt(CH.sub.3).sub.3, cyclopentadienyl (allyl)platinum (C.sub.5 H.sub.5)Pt(C.sub.3 H.sub.5), cyclopentadienyl(methylallyl)platinum (C.sub.5 H.sub.5)Pt(CH.sub.3 C.sub.3 H.sub.4) and methylcyclopentadienyl(methylallyl)platinum (CH.sub.3 C.sub.5 H.sub.4)Pt(CH.sub.3 C.sub.3 H.sub.4).
Among these compounds, those having melting points reported in Dictionary of Organometallic Compounds, Vol. 3, (2nd Ed. 1996, Chapman & Hall), etc. are listed in Table 1.
TABLE 1 ______________________________________ Melting points of compounds M.p. Compound Chemical formula (.degree. C.) ______________________________________ trimethyl(cyclopentadienyl)platinum (C.sub.5 H.sub.5)Pt(CH.sub.3).sub.3 105 trimethyl(methylcyclopentadienyl) (CH.sub.3 C.sub.5 H.sub.4)Pt(CH.sub.3).sub.3 30 platinum cyclopentadienyl(allyl)platinum (C.sub.5 H.sub.5)Pt(C.sub.3 H.sub.5) 63-64 dimethyl(cyclooctadiene)platinum (C.sub.8 H.sub.12)Pt(CH.sub.3).sub.2 94-95 methyl(carbonyl)cyclopentadienylplatinum (C.sub.5 H.sub.5)Pt(CH.sub.3)(CO) &lt;-20 trimethyl(acetylacetonato)platinum (C.sub.5 H.sub.7 O.sub.2)Pt(CH.sub.3).sub.3 solid bis(acetylacetonato)platinum Pt(C.sub.5 H.sub.7 O.sub.2).sub.2 250 ______________________________________
As Table 1 shows, the compounds except methyl(carbonyl)cyclopentadienylplatinum are each in the form of a solid at room temperature of 25.degree. C. On the other hand, methyl(carbonyl)cyclopentadienylplatinum is unfavorable as a feedstock in mass production, since it has CO and shows a somewhat poor storage stability.
The supply of the starting compound by sublimation in the CVD method is inferior in quantitative supply, regulation and mass-productivity to the liquid supply system or evaporation supply system with the use of a carrier gas bubbling into the liquid. If the starting compound can be liquefied by heating, it can be supplied by evaporation and thus the regulation can be significantly improved. Even in this case, however, the systems and apparatuses usable therein are considerably restricted as compared with the case where the starting compound can be handled in the form of a liquid at room temperature. Accordingly, it is required to employ a starting compound which is a liquid at room temperature and shows a sufficient vapor pressure after heating. However, there is no publicly known compound which is usable in Pt film formation by the CVD method, is in the stable form of a liquid at room temperature of 25.degree. C. and has a vapor pressure.
One of the problems to be solved by the present invention is to disclose a compound which is usable in Pt film formation by the CVD method, is in the stable form of a liquid at room temperature of 25.degree. C. and has a vapor pressure and to provide a process for producing Pt films by the CVD method with the use of the compound. The present invention further aims at providing a process for producing the above compound.